The present invention relates generally to chokes and more specifically to a choke for a pneumatic brake control valve.
Pneumatic brake control valves, for example the DB60 available for New York Air Brake Corporation and other brake valves, include a number of chokes or restrictions which control the rate of flow from air pressure source to a chamber. With the increased use of electropneumatic brake control valves, the pneumatic portion has been redesigned. This redesign has resulted in severe space limitations while still requiring that the performance characteristic be met. For example, the flow of pressure of a reservoir into a control volume or chamber during an emergency brake application must have a controlled build-up slow enough to satisfy the 7 to 12 second rate requirement. This is the emergency reservoir to the control volume for the brake relay.
One of the factors that determines the flow rate of the valve is the diameter of the orifice and the length of the orifice. Experiments has shown that the size or effective diameter has a practical lower limit of about 0.020 inches. This yields about a 4.5 second rate. Increasing the choke length to ⅝ of an inch only increases the rate to a little over 5 seconds. Space limitations for the control valve prevents the length from being increased much if at all about a ⅝ of an inch. Not to mention, it is very difficult to manufacture a 0.020 inch by ⅝ of an inch hole.
The present invention provides an appropriate choke for a brake control valve coming within the physical space limitation by forming a helical choke path. The choke includes a body having a passage and a plug in a passage. The helical path is created between and defined by the passage and the plug to form the choke. The length the passage is less an inch and the length of the plug is less than 0.25 inches. The helical path is in the surface of one or both of the passage and the plug. The effective diameter of the helical path is below 0.02 inches. The length of the helical path is in the range of 1 to 4 inches. The plug is preferable press fitted into the passage.
The body includes the first portion having an external thread and a stem portion. The helical path is in the first portion which receives the plug. A filter is mounted on the stem portion. The stem includes a circumferential recess and a gasket in the recess. The stem portion may also have a polygonal exterior cross-section. The first portion is mounted in a threaded opening in a first wall of the valve. The filter extends into an opening in a second wall of the valve and a cap mounted in the second opening contacts the filter and holds it secure on the stem.